Device for preventing pipe buckling

ABSTRACT

An apparatus for preventing pipe buckling when downwardly directed axial forces are applied to a pipeline ( 3 ) which extends from a derrick ( 1 ) down into a well bore, especially when snubbing. The apparatus comprises two sets of pipe supports ( 8 ) linked together to give a continuous chain ( 10 ), which is arranged to extend from a respective guide rail ( 6, 7 ) in the derrick ( 1 ) to the pipeline ( 3 ), and the pipe supports ( 8 ) are movably arranged in the guide rail ( 6, 7 ) parallel to the pipeline ( 3 ). The guide rail ( 6, 7 ) extends in a general U-shape with the U-bend ( 6   c   , 7   c ) located closest to the lower end of the derrick ( 1 ) and comprises two legs ( 6   a   , 6   b   , 7   a   , 7   b ), of which a first leg ( 6   a   , 7   a ) is arranged close to the pipeline ( 3 ) and a second leg ( 6   b   , 7   b ) is arranged at a greater distance from the pipeline. The pipe supports ( 8 ) are designed to be placed in the first leg ( 6   a   , 7   a ) when operative, and are designed to be transferred to the second leg ( 6   b   , 7   b ) when they are to be rendered inoperative.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for preventing pipebuckling when downwardly directed axial forces are applied to a pipelinewhich extends from a derrick down into a well bore, especially whensnubbing.

Snubbing is carried out when a drill pipe or production tubing must beforced down into the well against well pressure, and the well pressureis so great that the pipe does not run down by virtue of its own weight.A axial force is then applied to the pipe, forcing the pipe down againstwell pressure. During snubbing of this kind there is a danger that thepipe might buckle sideways halfway between the top drive, which holdsthe pipe at its upper end, and the drill deck. The buckling may be sogreat that the pipe breaks.

In the case of a pipeline consisting of pipes having a diameter of 2⅞″(7.3 cm), the buckling length during snubbing is about 70 cm. This meansthat the pipe must be gripped at intervals of 70 cm in order to apply anaxial force. In the case of a pipe length in the derrick, between thedrill deck and the top drive, of a total of 9 m, this means that thepipe must be gripped about 13 times to prevent the pipe from breaking.Of course, this takes considerably longer than it would had it beenpossible to run down the whole pipe length in the derrick at one go.

SUMMARY OF THE INVENTION

The object of the present invention is to make this possible. In orderto secure this object, the apparatus comprises a plurality of pipesupports which are arranged to extend from a guide rail in the derrickto the pipeline, and the pipe supports are movably arranged in the guiderail parallel to the pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings, wherein:

FIG. 1 shows a derrick equipped with an apparatus according to theinvention, with pipe supports in engagement with the pipeline;

FIG. 2 shows the apparatus according to FIG. 1, with the pipe supportspulled away from the pipeline;

FIG. 3 shows the apparatus according to FIGS. 1 and 2 where the pipesupports have be moved completely out of the path of travel of the topdrive;

FIG. 4 shows the apparatus according to the invention removed from thederrick;

FIG. 5 shows the apparatus according to the invention seen from above;and

FIG. 6 is a detailed view of a pipe support.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic illustration of a derrick 1, in which there islocated a top drive 2, which is arranged to grip a pipeline 3 at theupper end thereof with the aid of a holder 4. FIG. 1 also shows anapparatus 5 in accordance with the present invention. The apparatus 5comprises a pair of guide rails 6 and 7, each being generally U-shapedand including legs 6 a, 7 a, 6 b, 7 b and a U-bend 6 c, 7 c. In theillustrated exemplary embodiment, the legs 6 a, 6 b, 7 a, 7 b areparallel. A plurality of pipe supports 8 are movably arranged in theguide rails 6 and 7 and are linked together via articulations 9 to givea continuous pipe support chain 10.

The pipe support chain 10 is connected via an articulation 11 to the topdrive 2 and follows this during the vertical movements thereof.

The guide rails 6 and 7 are suspended in the derrick via suspensionrails 12, suspension stays 13 and hydraulic cylinders 14. There is atotal of four suspension rails 12, two suspension stays 13 and fourhydraulic cylinders 14. The hydraulic cylinders 14 are arranged to pullthe guide rails 6 and 7 away from the pipeline 3 and move the guiderails 6 and 7 back towards the pipeline 3 again. The guide rails 6, 7engage with nonillustrated rollers in the suspension rails 12 and rollalong these when they are moved away from and towards the pipeline 3.The suspension stay 13 is pivotally arranged in the derrick 1. In FIG.2, the guide rails 6 and 7 are moved a small distance away from thepipeline 3.

In FIG. 3 the guide rails 6 and 7 are moved completely out of the pathof travel of the top drive 2. The guide rails 6 and 7 are then movedtowards the extreme end of the suspension rails 12, and the pipe supportchain 10 is moved from the guide rail leg 6 a, 7 a, via the U-bend 6 c,7 c to the guide rail leg 6 b, 7 b. The articulation 11 is disconnectedfrom the top drive 2. It is now possible to carry out operations in thederrick which do not require the apparatus according to the invention,and where the apparatus will not be in the way either.

FIG. 4 shows the apparatus according to the invention removed from thederrick to better illustrate the details thereof.

FIG. 5 shows the apparatus of the invention from above, and here thesame reference numerals are used for the same parts as in the precedingfigures.

FIG. 6 shows a pipe support in detail. The pipe support 8 comprisesguide rail rollers 15, which are arranged for engagement with the guiderail 6, 7 at one end thereof, and at the opposite end thereof comprisesa roller 16 having a concave surface 17 for contact with the pipeline 3.

When the apparatus according to the invention is in use, the situationshown in FIG. 1 arises. The pipe supports 8 will be pressed against thepipeline 3 with a force determined by the hydraulic pressure of thecylinders 14. Owing to the concave surface 17 of the rollers 16, thepipeline 3 will in fact be prevented from buckling transverse to thelongitudinal extent of the pipe supports 8, even though pipe supports 8are only arranged in pairs. As the top drive 2 presses the pipeline 3downwards, the top drive 2 will move downwards in the derrick. Since thepipe support chain 10 is physically connected to the top drive 2, thepipe support chain 10 will also move downwards together with thepipeline 3. As the pipe support chain 10 moves downwards, the lowermostpipe supports 8 will be pushed into the U-bend 6 c, 7 c and then upwardsin the guide rail leg 6 b, 7 b.

It is preferable to attempt to position the pipe connections in thespaces between two pipe supports 8, but it is also possible to equip thepipe supports with an elastic device, so that the pipe supports whichmay come to bear against a pipe connection, spring slightly backwardsrelative to the other pipe supports.

Owing to the rollers 16, there will be no sliding movement between thepipeline and the pipe supports even though there might be a certainrelative movement therebetween, for example, because of slack,compression of the pipe or the like.

The embodiment described above is merely intended to serve as anexemplary embodiment, and changes may of course be made to this withinthe scope of the present invention. For instance, the pipe supports donot necessarily need to be linked together in a continuous chain, butthey could move individually and synchronously by means of, for example,small motors positioned in connection with each pipe support. In thatcase, the pipe supports do not necessarily need to be physicallyconnected to the top drive, but synchronisation therewith may, forexample, be attained by means of an electronic control. The guide railsmay also be suspended in the derrick in some other way, or be fixedlymounted therein, the pipe supports then preferably being designedtelescopically, so that their outer ends can be pulled away from thepipeline.

What is claimed is:
 1. An apparatus for preventing pipe buckling whendownwardly directed axial forces are applied to pipeline (3) whichextends from a derrick (1) down into a well bore, comprising a derrick(1) having at least one guide rail and a plurality of pipe supports (8)which are arranged to extend from a guide rail (6, 7) in the derrick (1)to the pipeline (3), and that the pipe supports (8) are movably arrangedin the guide rail (6, 7) parallel to the pipeline (3), characterised inthat the pipe supports (8) are linked together to give at least onecontinuous chain (10), wherein the guide rail (6, 7) extends in ageneral U-shape with the U-bend (6 c, 7 c) located closest to the lowerend of the derrick (1) and that the pipe supports (8) are arranged to bemoved out of contact with the pipeline (3) by being transferred into theU-bend (6 c, 7 c).
 2. The apparatus according to claim 1, characterisedin that it comprises two sets of pipe supports (8) which are arranged toextend from guide rails (6, 7) placed on opposite side of the pipeline(3).
 3. The apparatus according to claims 1, characterised in that theguide rail (6, 7) comprises two legs (6 a, 6 b, 7 a, 7 b), of which afirst leg (6 a, 7 a) is arranged close to the pipeline (3) and a secondleg (6 b, 7 b) is arranged at a greater distance from the pipeline, thepipe supports (8) being designed to be placed in the first leg (6 a, 7a) when operative and designed to be transferred to the second leg (6 b,7 b) when they are to be rendered inoperative.
 4. The apparatusaccording to any claim 1, characterised in that the guide rail (6, 7) ismovable transverse to the axis of the pipeline (3).
 5. The apparatusaccording to claim 1, characterised in that the guide rail (6, 7) issuspended in at least one suspension rail (12) which extends generallytransverse to the guide rail (6, 7).
 6. The apparatus according to claim1, characterised in that the guide rail (6, 7) is suspended in at leastone suspension stay (13), which is pivotally supported in the derrick(1).
 7. The apparatus according to claim 1, characterised in that thepipe supports (8) are connected to a top drive (2) in such a way thatthe pipe supports (8) follow the vertical movement of the top drive (2).8. The apparatus according to claim 1, characterised in that each of thepipe supports (8) at each of their ends facing the pipeline (3) isequipped with at least one roller (16) having a concave contact face(17) against the pipeline (3).
 9. The apparatus according to claim 3,characterised in that it comprises two sets of pipe supports (8) whichare arranged to extend from guide rails (6, 7) placed on opposite sidesof the pipeline (3).
 10. The apparatus according to claim 3,characterised in that the guide rail (6, 7) is moveable transverse tothe axis of the pipeline (3).
 11. The apparatus according to claim 3,characterised in that the guide rail (6, 7) is suspended in at least onesuspension rail (12) which extends generally transverse to the guiderail (6, 7).
 12. The apparatus according to claim 1, characterised inthat the guide rail (6, 7) is suspended in at least one suspension stay(13), which is pivotally supported in the derrick (1).
 13. An apparatusaccording to claim 1, characterised in that the pipe supports (8) areconnected to a top drive (2) in such a way that the pipe supports (8)follow the vertical movement of the top drive.
 14. The apparatusaccording to claim 1, characterised in that each of the pipe supports(8) at each of their ends facing the pipeline (3) is equipped with atleast one roller (16) having a concave contact face (17) against thepipeline (3).